(1) Field of the Invention
This invention relates to a locking device for vehicle seat belt webbing.
(2) Description of the Prior Art
As a retractor for taking up the webbing of a seat belt mounted on a vehicle to restrain its occupant, there has heretofore generally been used a retractor, which normally permits free pay-out and take-up of the webbing and is equipped with emergency locking mechanism so as to prevent the pay-out of the webbing in case of emergency.
In many of such conventionally known retractors, the prevention of pay-out of the webbing is generally done by winding the webbing up on a reel journalled on a housing and stopping the rotation of the reel by locking means in case of emergency. They are thus accompanied by a drawback that the occupant may not be satisfactorily protected as the webbing is not per se directly locked and may still be paid out of the retractor by a length equivalent to that available from tightening a webbing portion wound up on the reed even after the rotation of the reel has been stopped. This drawback is a serious problem when such a conventional retractor is mounted on a small car, the interior space of which is inherently limited. Namely, since the distance between an occupant of a small car and the steering wheel, instrument panel or windshield thereof is rather short, the occupant may hit the steering wheel or the like and be seriously hurt by a pay-out of the webbing due to the tightening of the webbing portion on the reel. The cope with the above-described problem, it has recently been proposed to directly lock the webbing per se at the outlet of a retractor.
However, such a retractor has been found unsatisfactory as its webbing is kept in frictional contact with clamping means even during its normal use and cannot be handled smoothly. A further proposal has also been made with a view toward solving the above new problem by providing many guide rollers in the vicinity of the clamping means. Although the latter proposal was successful to an extent in improving the handling of the webbing, it has been found to be still unsatisfactory due to complication of its structure resulting from the arrangement of many rollers and increased frictional resistance at the rollers.
As examples of locking devices equipped with many guide rollers, reference may be made to U.S. Pat. Nos. 3,439,932 and 3,442,529 issued respectively Apr. 22 and May 6, 1960 to Gerald R. Lewis et al. These U.S. patents disclose a counterweight in place of a reel-type retractor which is generally used for automobile seat belts. Needless to say, the locking device described in each of these U.S. patents may be applied in combination with such a reel-type retractor. In the above U.S. patents, a pair of mutually opposing guide rollers are provided. One of the guide rollers is fixed while the other guide roller is disposed displaceable relative to the former guide roller. Both rollers are provided with clamp members, between which the webbing is clamped when the other roller is displaced toward its counterpart roller. The locking of the webbing is dependent on the clamp means only, because the guide rollers are not locked but allowed to rotate. Thus, the webbing may not be sufficiently locked. Furthermore, the webbing may be cut up by the clamp members because the locking force is not distributed by rather centralized.
As another example of prior art locking devices, U.S. Pat. No. 4,128,261 issued Dec. 5, 1978 to Hannu O. Paitula and assigned to Granges Essem Aktiebolag Fack may be referred to. It discloses a locking mechanism comprising a stop means, a non-displaceable roller and a roller which is displaceable relative to both stop means and non-displaceable roller. Although the non-displaceable roller can be locked by a locking device, which is actuated by a sudden acceleration or deceleration of a vehicle, the displaceable roller is not provided with any locking means. Thus, the circumferential surface of the displaceable roller may not be used effectively for restraining the webbing from being paid out. In view of the configurations of the stop means and both rollers, the restraining force is exerted on the webbing principally at two locations only, in other words, between the stop means and displaceable roller and between the displaceable roller and non-displaceable roller, thereby involving a potential danger that the webbing may be cut up there.
U.S. Pat. No. 3,871,599 issued Mar. 18, 1975 to Takezo Takada and assigned to Takata Kojyo Co., Ltd. discloses a locking mechanism, in which the rotation of a guide roller equipped with gears is stopped by means of a locking member having racks and a clamp member. However, the interlocking between the guide roller and the locking member is performed via the webbing, thereby making the locking of the guide roller insufficient. As in the above prior art references, the webbing is clamped at a narrow area between the guide roller and clamp member and it is thus open to considerable damage. In addition, the webbing is bent at a sharp angle by the clamp member and the locking force is centralized at the bent portion. Therefore, the webbing is susceptible of being cut up at the bent portion.
Finally, U.S. Pat. No. 4,249,708 issued Feb. 10, 1981 to Schuichi Asano and assigned to Nippon Seiko Kabushiki Kaishi is also referred to. It discloses an emergency locking mechanism adapted to lock a roller per se. This mechanism appears to be more effective than those disclosed in the above prior art references in that it makes an effective use of the contact between the circumferential surface of the roller and the webbing to restrain the webbing from being paid out. However, similar to the above prior art locking devices or mechanisms, the contact between the roller and fixed plate which serves as a clamp member takes place in the form of a line, thereby resulting in a centralization of the clamping force and possibly leading to the cutting of the webbing.